1. Field of the Invention
The present invention relates to a thermosetting resin composition for prestressed concrete tendon used for anti-rust and anti-corrosion of a tendon that is used in a post-tension technique of a prestressed concrete, the composition being used also for integral bonding of the tendon and concrete, and the invention also relates to a use method thereof and a prestressed concrete tendon using the composition.
2. Description of the Related Art
A post-tension technique of a prestressed concrete is a technique in which prior to pouring a concrete, a metal- or resin-made sheath having inserted therein a tendon such as PC steel material (PC steel wire, PC steel twisted wire, PC steel rod or the like) is arranged for reinforcement in a concrete form, a concrete is poured into the concrete form, the tendon is strained after the concrete is set, and a cement milk or the like is poured into a space between the sheath and the tendon for the purpose of anti-rust and anti-corrosion of the tendon and also adhesion and integral bonding of the tendon and concrete.
However, in this conventional technique, works of inserting the tendon in the sheath and pouring a cement milk are complicated works and require much time and labor. Further, because a space between the tendon and the sheath is very narrow, filling the space with the concrete milk tends to be incomplete. Japanese Patent Application Laid-Open No. Sho 64-31873 proposes a technique of previously filling a curable composition in a space between a sheath and a tendon. Since in this technique, a curable composition is previously filled in a space between a sheath and a tendon, the space between the sheath and the tendon is completely filled. As a result, improvement in reliability and labor saving in a work site can be achieved.
However, it has been found that there is the following disadvantage in a large-sized concrete structure. Heat of hydration reaction generated in solidifying a concrete accumulates in the structure and a certain portion may reach a high temperature of 80xc2x0 C. or higher. As a result, if a tendon is arranged for reinforcement in the large-sized structure by applying the above conventional technique, the curable composition filling the space between the sheath and the tendon hardens during the period between a period that a temperature exceeding 80xc2x0 C. is maintained and a period of the subsequent natural cooling. Then when trying to strain the tendon, it is no longer possible to strain the tendon. Furthermore, it was found that the degree of accumulation of heat of hydration reaction generated in solidifying a concrete differs, and the peripheral temperatures of the tendon differ depending on the place, because the concrete structure in which the tendon is arranged, has a non-uniform thickness and the tendon hangs down when the concrete structure in which tendon is arranged, is long in size.
Accordingly, a first object of the present invention is to provide a thermosetting resin composition for prestressed concrete tendon, having the desired performances such that, even if a heat storage temperature in the concrete structure elevates from 30 to 85xc2x0 C. or higher, particularly a temperature reaching 95xc2x0 C., due to heat of hydration reaction in setting a concrete and this temperature is maintained until the completion of the reaction, the composition does not harden thereby being capable of straining the tendons after setting the concrete, and the composition including the site of 30xc2x0 C. or lower where there is substantially no partial heat storage due to heat of hydration reaction in solidifying the concrete, hardens after the passage of the prescribed time under spontaneous environmental temperature after the subsequent natural cooling, thereby achieving anti-rust and anti-corrosion of the tendons and also adhesion and integral bonding of the tendons and the concrete.
A second object of the present invention is to provide a use method of the thermosetting resin composition for prestressed concrete tendon, which can obtain a prestressed concrete structure having a desired performance by a post-tension technique using the thermosetting resin composition for prestressed concrete tendon.
A third object of the present invention is to provide a prestressed concrete tendon which is effective to obtain a concrete structure having the desired performances such that the composition does not harden, even if a heat storage temperature in the concrete structure elevates from 30 to 85xc2x0 C. or higher, particularly a temperature reaching 95xc2x0 C., due to heat of hydration reaction in setting a concrete and this temperature is maintained until the completion of the reaction, the composition does not harden thereby being capable of straining the tendons after setting the concrete, and the composition including the site of 30xc2x0 C. or lower where there is substantially no partial heat storage due to heat of hydration reaction in solidifying the concrete, hardens after the passage of the prescribed time under spontaneous environmental temperature after the subsequent natural cooling, thereby achieving anti-rust and anti-corrosion of the tendons and also adhesion and integral bonding of the tendons and the concrete by using the thermosetting resin composition for prestressed concrete tendon.
According to the present invention, there is provided a thermosetting resin composition for prestressed concrete tendon, comprising an epoxy resin, a latent hardener and a hardening accelerating diluent, the composition characterized by being previously heat treated at a temperature of 40 to 140xc2x0 C. The present invention further provides a use method of the thermosetting resin composition for prestressed concrete tendon, characterized in that the time of from pouring of concrete to straining of the tendon is 7 days or longer and the time of from pouring of concrete to hardening of the thermosetting resin composition is within 350 days.
Further, according to the present invention, there is provided the use method of the thermosetting resin composition for prestressed concrete tendon, characterized in that a maximum heat storage temperature due to hydration reaction of concrete is 80xc2x0 C. or higher, particularly 80 to 95xc2x0 C.
The present invention also provides a prestressed concrete tendon using the thermosetting resin composition for prestressed concrete tendon.
The present invention is described in detail below regarding a thermosetting resin composition for prestressed concrete tendon (hereinafter referred to as a xe2x80x9ccomposition of the present inventionxe2x80x9d), its use method and a prestressed concrete tendon using the composition of the present invention.
The composition of the present invention comprises an epoxy resin, a latent hardener and a hardening accelerating diluent as the essential components.
The epoxy resin which is one of the essential components in the composition of the present invention is a liquid resin having two or more epoxy groups in one molecule. Examples of the epoxy resin include polyglycidylated-products of polyhydric phenols such as 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl) ethane, bis(4-hydroxyphenyl)methane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, hydroquinone and resorcin.
The epoxy resin is preferably a resin purified such that a hydrolyzable chlorine content therein is reduced to less than 0.07% by weight, preferably 0.05% by weight, and particularly preferably 0.03% by weight. In the present invention, if the latent hardener described hereinafter is reacted with chlorine, hardening time prolongs. Therefore, it is advantageous that the content of the hydrolyzable chlorine is smaller.
Besides the epoxy resins listed above, other epoxy resins can be used in the composition of the present invention for the purpose of, for example, controlling a viscosity of the composition. Examples of the other epoxy resin that can be used include polyglycidylated products of polyhydric alcohols such as ethylene glycol, glycerin or trimethylol propane, and polycarboxylic acids such as phthalic acid.
Examples of the latent hardener include organic acid dihydrazides such as adipic acid dihydrazide or sebacic acid dihydrazide, diphenyldiaminosulfone, dicyandiamide, imidazole derivatives such as 2-methylimidazole and its derivative, ketimine and BF3-amine complex. Of those, organic acid hydrizides, dicyandiamide, imidazole derivatives and BF3.amine complex are preferable for the reason that those have very low reactivity at room temperature and this makes it possible to take a wide control range of curing time by heat treatment of the composition of the present invention.
The blending proportion of the latent hardener in the composition of the present invention varies depending on the kind of the epoxy resin and the hardener to be used, but the amount of the latent hardener having active hydrogen is preferably 1:0.3 to 2.0 in terms of molar ratio of epoxy group to active hydrogen, and since the ionic polymerizable catalyst type latent hardener such as BF3.amine complex or tertiary amine is a catalyst type, the amount thereof can generally be a small amount and is preferably 0.3 to 5 parts by weight per 100 parts by weight of the epoxy resin.
In the composition of the present invention, the hardening accelerating diluent has a role of diluting the epoxy resin and the latent hardener to accelerate hardening. In the composition of the present invention, the hardening reaction does not proceed with only the epoxy resin and the latent hardener. Although the hardening accelerating diluent is not particularly limited, at least one member selected from the group consisting of alcohol and its derivatives, ether, ester, ketone, amide, hydrocarbon and water is preferably used.
Specific examples of the alcohol include methanol, ethanol, isopropyl alcohol, butanol, isobutanol, cyclohexanol, 2-ethylhexanol, furfuryl alcohol and benzyl alcohol.
Specific examples of the alcohol derivative include ethylene glycol and ethylene glycol derivatives such as diethylene glycol, ethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol and propylene glycol derivatives such as propylene glycol monomethyl ether.
Specific examples of the ether include dioxane and tetrahydrofuran. Specific examples of the ester include n-butyl acetate, isobutyl acetate, esters of the above-described ethylene glycol derivatives and acetic acid, such as ethylene glycol monoethyl ether acetate, and esters of the above-described propylene glycol derivatives and acetic acid.
Specific examples of the ketone include methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone and isophorone. Specific example of the amide includes dimethyl formamide.
Specific examples of the hydrocarbon include toluene, xylene, cyclohexanone and mineral spirit.
Of those, ethylene glycol derivatives, propylene glycol derivatives, benzyl alcohol and cyclohexanone are preferable from the viewpoint that those are effective to control the hardening time by heat treatment of the composition of the present invention.
The blending proportion of the hardening accelerating diluent in the composition of the present invention is preferably 0.001 to 30 parts by weight, and more preferably 0.002 to 25 parts by weight, per 100 parts by weight of the epoxy resin. If the blending proportion of the hardening accelerating diluent is within this range, it is possible to control hardening time of the composition obtained, which is preferable.
Other than the above-described essential components, the composition of the present invention may contain various additives such as commercially available aerosil, nip seal or amide wax; modifiers such as xylene resin, dicyclopentadiene resin or coumarone resin; fillers such as talc, calcium carbonate, barium sulfate, clay, dolomite or silica; and coloring materials such as titanium dioxide, red iron oxide or phthalocyanine blue, in an amount of not impairing the effect of the present invention for the purpose of controlling a viscosity, imparting thixotropic property, improving strength of a hardened product, or the like.
The composition of the present invention can be produced by stirring and mixing the above-described epoxy resin, latent hardener and hardening accelerating diluent, and various components blended or added according to the need.
The blending proportion and the order of addition of those various component are not particularly limited. However, it is important for the epoxy resin, latent hardener and hardening accelerating diluent to be in a homogeneously dispersed state, and a method is preferable in which the latent hardener and the hardening accelerating diluent are blended with the epoxy resin in which the degree of dispersion of those component can be inspected, the resulting blend is mixed under stirring, and various components blended or added according to the need, are mixed with the above resulting mixture under stirring.
The composition of the present invention is heat treated at a temperature of 40 to 140xc2x0 C., preferably 60 to 120xc2x0 C., for a prescribed time after or during stirring and mixing the above-described each component, or under the state that the composition is processed into a prestressed tendon. By this heat treatment, it is possible to control a curing time of the epoxy resin and the latent hardener by the action of the hardening accelerating diluent, and the desired hardening characteristics according to the heat storage temperature pattern due to heat of hydration reaction in setting the objective concrete can be obtained. For example, heat treatment at 90xc2x0 C. for 24 hours can shorten the setting days of the thus treated composition by about 100 days or more as compared with the composition that is not heat treated, even an environmental temperature of 23xc2x0 C. in which there is almost no heat storage due to heat of hydration reaction in setting a concrete. If heat treatment at 90xc2x0 C. for 48 hours is applied, the setting days of such a composition can shorten by 200 days or more as compared with the composition that is not heat treated, even under the environment of 23xc2x0 C. in which there is almost no heat storage due to heat of hydration reaction in setting a concrete. On the other hand, the days that enables to strain the tendon are all 10 days or more even under the temperature pattern in which the heat storage temperature due to heat of hydration reaction in setting a concrete having a thickness of 90 cm becomes a temperature exceeding 90xc2x0 C., and this temperature is maintained, and the concrete is already sufficiently set when the tendon is strained.
Temperature of the heat treatment is important in obtaining the desired curability of the composition of the present invention, and the higher temperature is advantageous in that the composition having the desired curability can be produced within a short period of time. However, if the temperature exceeds 140xc2x0 C., the latent hardener is activated, and there is a fear of runaway reaction, which is not preferable. For example, the curability obtained by the heat treatment at 90xc2x0 C. for 24 hours substantially corresponds to the curability obtained by the heat treatment at 110xc2x0 C. for 3 hours.
The composition of the present invention can suitably be used in a post-tension technique as follows. The surface of a prestressed concrete tendon is coated with the composition of the present invention, or the composition of the present invention is charged into a space between a sheath and the tendon simultaneously with an insertion of the tendon in the sheath, the tendon incorporated in the sheath is arranged for reinforcement at a predetermined position of a concrete form, and a concrete is placed in the concrete form. After the concrete has reached the prescribed strength through hydration reaction of concrete, the tendon is strained. In this case, the time from placing of concrete to hardening of the thermosetting resin composition is preferably within 350 days from the viewpoint that a high strength and high durability inherently possessed by a concrete structure obtained by a post-tension technique can be secured at an early stage with high reliability.
Further, in the conventional art, if the maximum heat storage temperature due to heat of hydration reaction in setting a concrete is 80xc2x0 C. or higher, setting proceeds before the concrete reaches the predetermined strength in the conventional curable composition, and thus it was impossible to strain the tendon. However, by using the prestressed concrete tendon obtained such that the surface of the tendon is coated with the composition of the present invention, or the composition of the present invention is charged into a space between a sheath and the tendon simultaneously with an insertion of the tendon in the sheath, the heat storage temperature inside a concrete structure reaches 80xc2x0 C., preferably 80 to 95xc2x0 C., due to heat of hydration reaction in setting a concrete, and the composition does not cure even if the temperature is maintained until substantial completion of hydration reaction. Therefore, it is possible to strain the tendon after setting concrete. Further, the concrete structure having the intended performances can be obtained in which the composition including the site of 30xc2x0 C. or lower where there is substantially no partial heat storage due to heat of hydration reaction in setting the concrete hardens within the prescribed period of time under spontaneous environmental temperature after the subsequent natural cooling, thereby achieving anti-rust and anti-corrosion of the tendon and also adhesion and integral bonding of the tendon and the concrete.
In the method of using the composition of the present invention, the tendon, sheath and the like to be used are not particularly limited, and ordinarily used ones can be employed according to the purpose of use. In the case where heat treatment is conducted in the sate of processing into a prestressed concrete tendon such that the surface of the tendon is coated with the composition of the present invention and is then covered with a sheath, the sheath is preferably selected from materials having appropriate heat resistance. Although varying depending on the kind of material, heat resistance of the material used in the sheath is, for example, up to 90xc2x0 C. for a polyethylene, up to 110xc2x0 C. for a polypropylene and about 140xc2x0 C. for a polymethyl pentene.
Further, the prestressed concrete tendon using the composition of the present invention can be produced by coating the tendon comprising PC steel stock (PC steel wire, PC steel twisted wire, PC steel rod or the like) with the composition of the present invention, or filling the composition of the present invention in a space between the sheath and the tendon at the same time as the tendon is inserted. For example, the tendon comprising a prestressed concrete steel wire material in which the steel wire is inserted in a polyethylene-made sheath is continuously produced in a factory. In such a case, the thermosetting resin composition of the present invention is filled in a space between the sheath and the steel wire at almost the same time as the steel wire. The tendon comprising the prestressed concrete steel wire produced in a factory is transported to a construction site of concrete structures and arranged for reinforcement in a concrete form concrete is then poured into the concrete form, and after the concrete is set, the steel wire is strained and maintained. Thereafter, the thermosetting resin composition in the prestressed concrete steel wire material is hardened within the prescribed time to integrally bond the concrete and the tendon. Also corrosion of the tendon is prevented and as a result, concrete structures having high reliability can be produced.